Referring to FIG. 1 and FIG. 2, the conventional method for manufacturing a polysilicon with a small line width includes steps of: 1) forming an insulator 11 on a substrate 10; 2) depositing a polysilicon 12 on the insulator 11 by chemical vapor deposition (CVD); 3) coating a layer of photoresist 13 on the polysilicon 12 and then forming the photoresist with a pattern having an interval x and a width y after exposure and development of photolithography; 4) removing a portion of the polysilicon 12 that is not covered by the photoresist 13 by etching technique to form the polysilicon 12 with the same pattern. However, the minimum interval x and line width y of the polysilicon depends on the smallest pattern which can be developed by photolithography and etched by etching technique. In order to fabricate the polysilicon with relatively small interval x and line width y, it requires a preferable photolithography technology. Up to the present day, the photolithographis process for manufacturing the polysilicon with small line width includes: a) using I-line (365 nm) matched with the photoresist with high resolution; b) using the phase-shifting mask; and c)using deep UV (248 nm). Nevertheless, although the photolithography using short wavelength and phase-shifting mask can be used for manufacturing a polysilicon with small line width, there are some demerits described as follows:
1. The costs for the instrument of photolithography with short wavelength and the phase-shifting mask are very expensive. PA1 2. The phase-shifting mask is not easily fabricated.